https://www.science.org/doi/10.1126/sciadv.adr2722

Late acquisition of erect hindlimb posture and function in the
forerunners of therian mammals

Abstract
The evolutionary transition from early synapsids to therian mammals
involved profound reorganization in locomotor anatomy and function,
centered around a shift from “sprawled” to “erect” limb postures. When
and how this functional shift was accomplished has remained difficult to
decipher from the fossil record alone. Through biomechanical modeling of
hindlimb force-generating performance in eight exemplar fossil
synapsids, we demonstrate that the erect locomotor regime typifying
modern therians did not evolve until just before crown Theria. Modeling
also identifies a transient phase of increased performance in therapsids
and early cynodonts, before crown mammals. Further, quantifying the
global actions of major hip muscle groups indicates a protracted
juxtaposition of functional redeployment and conservatism, highlighting
the intricate interplay between anatomical reorganization and function
across postural transitions. We infer a complex history of synapsid
locomotor evolution and suggest that major evolutionary transitions
between contrasting locomotor behaviors may follow highly nonlinear
trajectories.

Nothing really new here, but a detailed account of when and how the many
adaptions that led from sprawled to upright posture in mammals. A
similar study on the same adaptations in the reptile lineage would also
be very interesting.